Or you can calculate it and only trim your wire only once
234 / resonate frequency - 234 / desired frequency = amount to trim (or add
if negative)
This will also work with a dipole if you trim off this amount from each
side.
John KK9A / P40A
To: <towertalk@contesting.com>
Subject: Re: [TowerTalk] 160m inverted l
From: "Dale Martin"
Date: Sat, 9 Dec 2006 14:05:08 -0600
If you've got an antenna analyzer like the MFJ-359, you can see where the
SWR is minimum. Cut off a few inches of antenna. See where the new minimum
SWR point is. Then you can figure how many kHz per inch the minimum SWR
point will move with each subsequent cut.
For instance, cut off 6 inches of antenna and find the minimum SWR moves
from 1818 to 1824. So, the kHz per inch is 1 kHz per inch. If you take off
six more inches, the minimum SWR moves to 1830, or 10 inches to move to
1834, etc.
Of course, it pays to be conservative when your are cutting wires, so always
cut for a lower frequency than the actual target until you get with a couple
of inches.
For my 1/4-wave half-sloper on 80, instead of cutting the wire to move it
into the phone band, I simply bring the antenna end back on itself to
shorten the overall antenna. I use the same method of calculating how much
will move how far, but without cutting the wire. :-)
73,
Dale, kg5u
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